Not Applicable
Not Applicable
1. Field of the Invention
The present invention relates to liquid product filling heads, more particularly, to a pneumatic control unit for automatically shutting off a liquid product filling head filling a container upon sensing that the container is full.
2. Description of the Related Art
There are a number of automatic container filling machines in the art wherein a sensing tube extends into a container to be filled and when the lower end of the tube is blocked by the product in the container, back pressure through the tube actuates a control device to stop the flow of product into the container. In particular, U.S. Pat. No. 5,161,586 discloses a pneumatic control unit that responds to a sensed back pressure to shut off liquid to the filling container. The shortcomings of the disclosed design are discussed in detail below relative to the present invention.
An object of the present invention is to provide a pneumatic control unit for a liquid filling head that is easier and less expensive to manufacture and that is easier to maintain than pneumatic control units of the prior art.
The present invention is a pneumatic control head for controlling the supply of a product into a container via a filling head with a sensing tube that extends into the container. The control head has a manifold with several air inputs. A main air input receives main air at an operating pressure, typically at about 60 psi. A blow down air input receives blow down air for cleaning the filling head as needed. A filling head output connects to the sensing tube. A cylinder for operating the filling head attaches to the manifold.
The majority of the control unit is built in a manifold. The manifold has a pilot air duct for conducting pilot air at a pressure near that of the main air operating pressure. A start valve takes in the main air and outputs it to the pilot air duct when actuated by a mechanical switch. The switch includes a ball bearing captured by a collar whereby the switch is actuated when the ball bearing is pressed into the collar.
A pilot valve in the manifold takes in the main air and allows it into a cylinder air duct to activate the cylinder in response to air pressure in the pilot air duct. Optionally, there is a no container switch that exhausts air from the pilot air duct in the event that there is no container under the filling head.
A flow regulator mounted to the manifold receives sensing air and outputs regulated sensing air at a sensing pressure. Optionally, a sensing air shut off valve precedes the flow regulator. The sensing air shut off valve is controlled by the main air to the cylinder so that if the cylinder is not actuated, there is no sensing air to cause the filling product to bubble.
The regulated sensing air passes through a filling head source valve to a filling head output. Normally the filling head source valve routs the regulated sensing air to the filling head output. The filling head source valve routs blow-down air to the filling head output in response to main air from a blow down valve. The blow down valve takes in the main air and outputs it to a switch the filling head source valve when actuated by a mechanical switch. The switch is of the same design as that of the start valve.
An overpressure valve mounted to the manifold exhausts the pilot air duct in response to the regulated sensing air having a pressure higher than normal. When the product fills the container to the point that the product nearly contacts the sensing tube, a back pressure is created that causes the overpressure sensor valve to trip.
Physically, the control unit includes a manifold within which are cut holes for valves and channels for ducts. A top plate houses the flow regulator and provides a mount for the overpressure sensor valve.
The start and blow down valve switches are improvements over those of the control units of the prior art. Each switch is a ball bearing captured by a collar. An external cam pushes the ball bearing into the collar, causing the ball bearing to push the start valve. Friction is reduced because the ball bearing rotates within the collar as the cam slides by. The improvement includes significantly fewer moving parts that substantially reduces both the initial manufacturing and the periodic maintenance costs.
Another improvement over the prior art is the means by which two of the ducts are routed to their respective valves. The pilot and filling head source valves fit into openings in the manifold. The appropriate duct exits at an aperture adjacent to the valve. A single machined plate has a depression that overlaps the aperture and the valve opening. An o-ring fits into a groove surrounding the depression and valve opening. The o-ring provides a seal between the plate and the manifold when installed.
Other objects of the present invention will become apparent in light of the following drawings and detailed description of the invention.